Downsampling when exporting as JPEG has gotten screwed up in 19.1.0. Confirmed on two different machines with different versions of Windows. Old Photoshop (2017 something something) - open our PSD in 2048, export as JPEG scaled down 50% (to 1024), new JPEG aligns almost perfectly to PSD. New Photoshop - same pipeline: open our PSD in 2048, export as JPEG scaled down 50% (to 1024), new JPEG is visibly shifted down one pixel. Same exact exportation and sampling settings. This is a big, big no no for texture creation for 3D assets.

I looked at an image similar to yours and there is a 1 pixel shift, but in the left to right direction. I think what you are seeing is due to the interpolation method used. Bicubic and Bilinear sample the surrounding pixels to come up with the new pixels. Dependind on the image it could easily shift it by 1 pixel. Try using Nearest Neighbor in the Save As Resample setting. On my image it doesn't create any visible shift, but it can create stair-step artifacts.

No, see original post. It's not the method used. We used the same exact method in 2017 and it did not cause this. Furthermore, we went through every single interpolation option and they all produced the same result.

So how does this all work? Does Adobe actually check these posts? Because as far as I can tell there's no way to file tickets or speak to a live human being over there :\.

Yes Adobe Engineering does monitor these posts. I can't duplicate your exact 1 pixel down shift using my own image files. I suggest uploading an original PSD file that exhibits the issue along with Export As 50% Scaled JEPG files from PS 2017 and the latest PS version 19.1.0 to Dropbox. Provide the links here and I'll investigate further. Please also provide a screenshot of the 'Export As' settings window so I can use your exact settings.

In the interim you can try resetting the PS Preferences file to see if that corrects the issue. Close PS and then rename the Adobe Photoshop CC 2018 Prefs.psp with a .OLD extension as below. This will allow restoring it if the issue persists. When PS is launched a new Preferences file will be created with the default settings. Don't change any of its settings, but do try the Save As Export again and see if the results change.